Encyclopædia Britannica, Ninth Edition/Aneurism

ANEURISM (from ἀνεύρυσμα, a dilatation), a cavity, which contains blood, either fluid or coagulated, and which communicates with an artery; the walls of the cavity are formed either of the dilated artery or of the tissues around the vessel. This affection, a malady of middle life and old age, may arise in consequence of injury or disease of the blood-vessels.